stm32 USART

stm32 USART

1 USART基础知识

三种模式：轮询模式、中断模式、DMA模式

轮询模式属于阻塞模式

中断模式和DMA模式属于非阻塞模式

发送数据

接收数据

1.1 Polling mode IO operation

• Send an amount of data in blocking mode using HAL_UART_Transmit()
• Receive an amount of data in blocking mode using HAL_UART_Receive()

1.2 Interrupt mode IO operation

• Send an amount of data in non blocking mode using HAL_UART_Transmit_IT()
• At transmission end of transfer HAL_UART_TxCpltCallback is executed and user can add his own code by customization of function pointer HAL_UART_TxCpltCallback
• Receive an amount of data in non blocking mode using HAL_UART_Receive_IT()
• At reception end of transfer HAL_UART_RxCpltCallback is executed and user can add his own code by customization of function pointer HAL_UART_RxCpltCallback
• In case of transfer Error, HAL_UART_ErrorCallback() function is executed and user can add his own code by customization of function pointer HAL_UART_ErrorCallback

1.3 DMA mode IO operation

• Send an amount of data in non blocking mode (DMA) using HAL_UART_Transmit_DMA()
• At transmission end of half transfer HAL_UART_TxHalfCpltCallback is executed and user can add his own code by customization of function pointer HAL_UART_TxHalfCpltCallback
• At transmission end of transfer HAL_UART_TxCpltCallback is executed and user can add his own code by customization of function pointer HAL_UART_TxCpltCallback
• Receive an amount of data in non blocking mode (DMA) using HAL_UART_Receive_DMA()
• At reception end of half transfer HAL_UART_RxHalfCpltCallback is executed and user can add his own code by customization of function pointer HAL_UART_RxHalfCpltCallback
• At reception end of transfer HAL_UART_RxCpltCallback is executed and user can add his own code by customization of function pointer HAL_UART_RxCpltCallback
• In case of transfer Error, HAL_UART_ErrorCallback() function is executed and user can add his own code by customization of function pointer HAL_UART_ErrorCallback
• Pause the DMA Transfer using HAL_UART_DMAPause()
• Resume the DMA Transfer using HAL_UART_DMAResume()
• Stop the DMA Transfer using HAL_UART_DMAStop()

2 重定向USART的输入与输出

参考1：

//* printf重定向
//!配置好printf重定向的源文件。（有一处需要结合实际替换）
//!开启usart中断时：需要在主循环之前手动开启接收中断：HAL_UART_Receive_IT(&huart1, (uint8_t *)aRxBuffer, 1);

#ifdef __GNUC__
#define PUTCHAR_PROTOTYPE int __io_putchar(int ch)
#else
#define PUTCHAR_PROTOTYPE int fputc(int ch, FILE *f)
#endif
//! 直接printf("HelloWorld");会导致打印不出来，自觉加/r/n
PUTCHAR_PROTOTYPE
{
    //具体哪个串口可以更改huart1为其它串口
    HAL_UART_Transmit(&huart1, (uint8_t *)&ch, 1 , 0xffff);
    return ch;
}

参考2：https://stackoverflow.com/questions/51515052/redefining-fputc-function-when-using-arm-none-eabi-toolchain

/*# 7- Retarget printf to UART (std library and toolchain dependent) #########*/

#if defined(__GNUC__)
int _write(int fd, char * ptr, int len)
{
  HAL_UART_Transmit(&huart1, (uint8_t *) ptr, len, HAL_MAX_DELAY);
  return len;
}
#elif defined (__ICCARM__)
#include "LowLevelIOInterface.h"
size_t __write(int handle, const unsigned char * buffer, size_t size)
{
  HAL_UART_Transmit(&huart1, (uint8_t *) buffer, size, HAL_MAX_DELAY);
  return size;
}
#elif defined (__CC_ARM)
int fputc(int ch, FILE *f)
{
    HAL_UART_Transmit(&huart1, (uint8_t *)&ch, 1, HAL_MAX_DELAY);
    return ch;
}
#endif

// OR:

// Add syscalls.c with GCC

#ifdef __GNUC__
#define PUTCHAR_PROTOTYPE int __io_putchar(int ch)
#else
#define PUTCHAR_PROTOTYPE int fputc(int ch, FILE *f)
#endif /* __GNUC__ */

/**
  * @brief  Retargets the C library printf function to the USART.
  * @param  None
  * @retval None
  */
PUTCHAR_PROTOTYPE
{
  HAL_UART_Transmit(&huart1, (uint8_t *)&ch, 1, HAL_MAX_DELAY);
  return ch;
}

3 USART中断

• 使用USART接收中断（根据接收数据的个数判断接收是否完成）连续接收数据时注意使用HAL_UART_Receive_IT(&huart1,buff,buffsize);重复使能中断。需要在中断回调函数的最后再使用HAL_UART_Receive_IT(&huart1,buff,buffsize);使能一次。

//The specific UART interrupts (Transmission complete interrupt, RXNE interrupt
//and Error Interrupts) will be managed using the macros
//__HAL_UART_ENABLE_IT() and __HAL_UART_DISABLE_IT() inside the
//transmit and receive process.

//【注】：实际上使能中断的（宏）函数是__HAL_UART_ENABLE_IT只不过该函数在HAL_UART_Receive_IT和HAL_UART_Transmit_IT中被调用了。

#define buffsize 5
uint8_t buff[10];

HAL_UART_Receive_IT(&huart1,buff,buffsize);//可以接收指定长度的字符。任意长度需要使用DMA

void HAL_UART_RxCpltCallback(UART_HandleTypeDef *huart){
    if(huart->Instance==USART1){

    }
    HAL_UART_Receive_IT(&huart1,buff,buffsize);
}

• 进入中断回调函数需要对USART的句柄进行判断。

if(huart->Instance==USART1){

}

4 其他

• 可以使用string.h对字符串进行处理、比较。

• 串口通信有多种模式：

  • 普通模式：HAL_UART_Transmit、HAL_UART_Receive
  • 中断模式：HAL_UART_Transmit_IT、HAL_UART_Receive_IT
  • DMA模式：

  注意：在传输数据量较大，且通信波特率较高（大于38400）时，如果采用中断方式，每收发一个字节的数据
  
  （CPU都会被打断，造成（PU无法处理其他事务。因此在批量数据传输，通信波特率较高时，建议采用DMA方式。

• 其他重要函数：

  __HAL_UART_ENABLE_IT(HANDLE,INTERRUPT) 使能串口中断

  __HAL_UART_GET_FLAG(HANDLE,INTERRUPT) 查询串口中断标志

  __HAL_UART_CLEAR_IDLEFLAG(HANDLE) 清除对应的串口空闲中断标志